One way of looking at the entire Internet routing architecture is a set of domains where within each domain there is an internal routing environment. Each domain is a single administrative domain, operated within a uniform set of routing policies, and is operated independently from any other domain. The domain is in effect an autonomous unit in the overall routing architecture, and is termed an Autonomous System (AS). Each particular AS appears to other ASs to have a single coherent internal routing plan and presents a consistent picture of what destinations are reachable through the particular AS. Each of these ASs is uniquely identified using an Autonomous System Number (ASN). An ASN could be assigned, for example, to a network service provider (NSP), a large company, a university, a division of a company, or a group of companies.
The inter-domain routing environment describes how domains interconnect, but avoids the task of maintaining transit paths within each domain. In the inter-domain space, a routing path to an address is described as a sequence of domains that must be transited to reach the domain that originates that particular address prefix. Today this inter-domain space is maintained using Version 4 of the Border Gateway Protocol (BGPv4), RFC 4271.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.